Wordpress: responsive embeds

functions.responsive_embeds.php

<?php

/*
	Wraps the video embed code so that it takes the full width of the parent element
	and resizes keeping it's aspect ratio.
	Just tested for Vimeo and YouTube iframes so far ...
*/

add_filter('embed_oembed_html', function($html) {
	
	// preg dimensions from iframe attributes
	$width = preg_replace('/.*width="(\d*)".*/', '\\1', $html);
	$height = preg_replace('/.*height="(\d*)".*/', '\\1', $html);
	
	// calculate percentage for padding bottom hack
	$padding_bottom_percent = ($height / $width * 100);
	
	// add style attribute to iframe tag
	$html_with_style = preg_replace('/<iframe/', '<iframe style="position: absolute; left: 0; top: 0; width: 100%; height: 100%;"', $html);
	
	// return wrapped iframe
    return '
		<div style="position: relative; padding-bottom: ' . $padding_bottom_percent . '%">
			' . $html_with_style . '
		</div>';
    
}, 10);